An electrical outlet box provides a termination point for wires carrying electrical current through buildings, houses, and other structures. Wiring entering an outlet box is typically connected to a particular electrical fixture such as a receptacle or switch. These fixtures may be mounted within the box for termination to an end extent of the wiring which is also inserted into the box. The box is then typically covered by a face plate having an opening therein to allow access to the receptacle outlet or the switch while preventing electrified components from being exposed. Outlet boxes may be employed in concealed-wiring installations in which they are located within a wall or ceiling. Alternatively, outlet boxes may be used in exposed-conduit wiring installations where they are exteriorly mounted to a wall, column or ceiling. For most electrical fixtures, the outlet box is spacious enough to accommodate sufficient length of excess wiring to allow a connected fixture to be removed from the outlet box and serviced without disconnecting the fixture from the wiring.
Outlet boxes are available in a variety of configurations and sizes. The selection of which type of box to use is dependant upon the specifics of the application. The particular configuration of the outlet box may depend on a combination of the specifics of the application and the governing electrical code at a worksite. Metal outlet boxes typically include wire insertion apertures in the form of "loom holes". Loom holes are insertion apertures, typically circular in shape, which provide a removable tab or "knockout" positioned thereover. The knockout is deflectably or removably connected to the outlet box and may itself may include a central aperture for inserting thinner wires therethrough.
To install the electrical fixture, an installer pulls one end of an electrical wire or cable, through a loom hole. An excess length of wire is pulled through the loom hole allowing for the electrical fixture to be attached to the conduit at a location outside the outlet box where the installer has more room to work. A metal clamp will be fastened over the inserted wire so as to prevent the wire from being pulled or falling out of the box. The free end of wire is connected to the electrical fixture which is then mounted adjacent the open face of the outlet box. The outlet box has sufficient volume and depth for excess wire to be packed into the box behind the fixture.
Often times, metal outlet boxes are manufactured and shipped having a metal clamp installed therein. The need to ensure a metal clamp remains in a metal box during shipping usually requires that a screw be inserted through the clamp and securely fastened through the box so that transportation vibrations will not shake the fastening screw loose from the box. Typically this is accomplished by fully installing a threaded screw fastener through both a clamp and box so that the clamp is tightly installed. However, once the box is installed at a worksite, an electrician or other worker will have to back each fastening screw outwards so that the clamp may be loosened enough to allow a wire to be installed through an aperture which it covers. Once enough wire has been pulled through the wire installer will tighten down on the clamp again to hold the wire in place. For worksites at which may such boxes are installed the task of backing out each fastening screw prior to the wires being inserted can become a laborious task adding to the time and cost for wiring the worksite.
Furthermore, the governing electrical code may dictate the number and size of wire insertion apertures. Such requirements are dictated by relevant certifying agencies such as Underwriters Laboratories (UL) and the Canadian Standards Association (CSA). Different applications require different standards for the outlet box's ability to contain sparks. For example, an outlet box for a residential application may have more wire insertion apertures than an outlet box for an industrial application. As a result of such directives, outlet boxes have been formed for industrial applications having a smaller number of wire insertion apertures than outlet boxes for, e.g. residential applications. Electrical parts manufacturers, suppliers, and installers must therefore provide and keep in supply of outlet boxes that meet the governing electrical codes for industrial applications and a separate supply of outlet boxes that meet the governing electrical codes for different applications.
It is desirable to provide metallic electrical outlet box that requires less installer time and effort to install. It is also desirable to provide a single metallic electrical outlet box that meets relevant codes while still preserving the available options to the installer depending on the particular application.